Lightroom Feature Request: Noise Reduction Mask

While the noise reduction engine circa LR3 has been a revelation I feel it can be improved further by adding a variation of the masking algorithm from the Sharpening module. Noise is more prominent in the shadows, so a luminosity mask built on the fly that could more directly target the darkest parts of the image while protecting highlight detail would be great. Functionally would be very similar to the Sharpening mask in that using the ALT/Option keywould let you which parts of the image were being masked vs. having NR applied.